He was once the most dominant figure in American politics, his approval rating an astounding 90 percent. But four years after leaving office, former President George W. Bush is playing no role in this year's campaign -- and many fellow Republicans seem happy to keep it that way.

His father, former President George H.W. Bush, and mother, Barbara Bush, officially endorsed Mitt Romney five weeks ago. His brother, former Florida Gov. Jeb Bush, also has backed the presumptive Republican nominee.

And while the former president is expected to formally support Romney at some point between now and Election Day -- perhaps in a written statement -- many Republicans doubt he will actively campaign for the party's ticket this fall.

His withdrawal from the political stage stands in contrast to his predecessor, former President Bill Clinton, who has plunged into campaigns large and small since leaving office, even a race for a state Senate seat in Buffalo, N.Y.

At a similar point in his post-presidency, Clinton tried to sway the 2004 presidential race, appearing -- just weeks after undergoing heart surgery -- arm-in-arm with the Democratic nominee, Sen. John Kerry, at a late-October rally before 100,000 people in Center City, Philadelphia.

"If this isn't good for my heart, I don't know what is,'' Clinton said.

A former Bush adviser, Mark McKinnon, explained the contrast this way: "Bill Clinton loves to be on the radar. George W. Bush does not."

Commenting via email, McKinnon added, "I don't speak for the president, but my view is: President Bush is working quietly on issues he cares about and doing so in a way that is serious, dignified and respectful. Being back in the political spotlight simply doesn't put the focus where he wants it these days."

A spokesman for the 43rd president declined to comment, and referred ABC News to the website of the George W. Bush Presidential Center for a sense of Bush's priorities these days. The center is dedicated to such causes as education reform and promoting democracy abroad.

Whatever Bush's motives for avoiding politics, independent political strategists say it is better for Romney and the Republican Party that he do so.

They pointed out that in November 2008, just before he left office, only 20 percent of voters approved of Bush's performance as president -- the lowest of any president since Gallup began asking the question in 1938. Although his numbers have rebounded somewhat since then, many Americans still view him negatively.

Democrats are more blunt.

"Frankly, Republican strategists do not want to remind the American people of those eight years of Bush's presidency -- the foreign policy entanglements and the policies that set the stage for the economic collapse," said Democratic strategist Mark Siegel.

"He is even divisive among people in Republican base," Siegel added. "You hear conservatives attacking his unfunded entitlement programs, [and] the fact that we got into wars but didn't pay for them."

Chris Lehane, part of the braintrust in Al Gore's unsuccessful 2000 campaign for president, said putting Romney and Bush together on the campaign trail would only play into President Obama's hands as he seeks relection.

"It's inherently problematic. Obama has this framework of 'moving forward,' not back," Lehane said. "I don't think anyone is a more powerful symbol of that past than President George W. Bush."

Indeed, as he nears the end of his first term, Obama still invokes Bush's policies with disdain.

As for Romney, he rarely talks up George W. Bush; instead he frequently jumps back to the 1980s to praise President Ronald Reagan. During the Republican primaries, Rick Santorum went so far as to apologize for backing Bush's centerpiece education reform, the "No Child Left Behind" law, when he was senator.

John McLaughlin, a veteran Republican strategist, said he thinks Bush still could help Romney politically if he was used the right way. One idea: having Bush campaign in Republican strongholds to boost GOP turnout on Election Day, he said.

But McLaughlin said it is better for Bush's legacy if he stays on the political sidelines. As long as Bush avoids the political wars, his standing among Americans will continue to rebound.